Collect objects from different files to one

// "copy-n-paste" pageItems
// from open docs named 1, 2, 3, ... , n
// to corresponding layers in new untitled doc
var docs = app.documents;
var docNames = [];
for (var i = 0; i < docs.length; i++) {
  docNames.push(docs[i].name);
  docNames.sort();
}
var targetDoc = app.documents.add();
for (var i = docNames.length - 1; i > -1; i--) {
  docs[docNames[i]].activate();
  var layer1 = targetDoc.layers.add();
  layer1.name = docNames[i];
  for (var j = 0; j < app.activeDocument.pageItems.length; j ++) {
    app.activeDocument.pageItems[j].duplicate(targetDoc.layers[docNames[i]]);
  }
}